Thanks for posting this. This does seem to correct a lot of the common stated problems with estimates of S by incorporating all the lines of evidence. It’ll be interesting to see how this is received in AR6.
I have updated the guesstimate model from my How Hot Will it Get piece to reflect the findings here. The scenarios are labelled as the WCRP estimates of climate sensitivity.
Overall, I don’t view this as especially good news.
The 95% confidence interval for S for the baseline case is 2.3K to 4.7K. Depending on the emissions scenario you put in, this implies a 5% chance of >6.3K-7K of warming on pre-industrial.
With robustness checks, the 95% CI for S is 2 to 5.7K. Depending on the emissions scenario, this implies a 5% chance of >7K-10K on pre-industrial.
From what I have read of their assumptions, the Baseline case seems more plausible, e.g. the robustness checks include an assumption of a uniform prior over S, which seems wrong. This suggests that the high chance of extreme warming suggested by Wagner and Weitzman is less likely. Still, the chance of >6K is way too high.
I suppose they’re roughly in line with my previous best guess. On the basis of the Annan and Hargreaves paper, on median BAU scenario the chance of >6K was about 1%. I think this is probably a bit too low because the estimates that ground that were not meant to systematically sample uncertainty about ECS. On the WCRS estimate, the chance of >6K is about 5%. (Annan and Hargreaves are co-authors on WCRS, so they have also updated).
One has to take account of uncertainty about emissions scenarios as well
Thanks for posting this. This does seem to correct a lot of the common stated problems with estimates of S by incorporating all the lines of evidence. It’ll be interesting to see how this is received in AR6.
I have updated the guesstimate model from my How Hot Will it Get piece to reflect the findings here. The scenarios are labelled as the WCRP estimates of climate sensitivity.
Overall, I don’t view this as especially good news.
The 95% confidence interval for S for the baseline case is 2.3K to 4.7K. Depending on the emissions scenario you put in, this implies a 5% chance of >6.3K-7K of warming on pre-industrial.
With robustness checks, the 95% CI for S is 2 to 5.7K. Depending on the emissions scenario, this implies a 5% chance of >7K-10K on pre-industrial.
From what I have read of their assumptions, the Baseline case seems more plausible, e.g. the robustness checks include an assumption of a uniform prior over S, which seems wrong. This suggests that the high chance of extreme warming suggested by Wagner and Weitzman is less likely. Still, the chance of >6K is way too high.
AR6, for the uninformed like me.
Very useful comment — thanks.
How do these tail values compare with your previous best guess?
I suppose they’re roughly in line with my previous best guess. On the basis of the Annan and Hargreaves paper, on median BAU scenario the chance of >6K was about 1%. I think this is probably a bit too low because the estimates that ground that were not meant to systematically sample uncertainty about ECS. On the WCRS estimate, the chance of >6K is about 5%. (Annan and Hargreaves are co-authors on WCRS, so they have also updated).
One has to take account of uncertainty about emissions scenarios as well